DESCRIPTION: (Adapted from the Application). The biophysical parameters governing the interaction between the LDL-receptor related protein (LOP) and its ligands will be investigated. LRP is a scavenger receptor that is known to bind over twenty ligands, many of which have been found in proteinaceous plaques in the brains of persons suffering from Alzheimer's Disease (AD). In particular, this laboratory is interested in the LRP-mediated clearance of thrombin-PNI complexes, because the balance between thrombin and PN1 is upset in AD, and experiments have show l that thrombin acts to inhibit neurite outgrowth and promote synapse loss while PN1 reverses these effects. This laboratory has shown that clearance via LRP is the major route for clearance of thrombin-PN1 complexes by astrocyte cells, and it is suspected that disruption of LRP clearance may play a role in disruption of the balance between thrombin and PN1 in AD. LRP also clears ApoE, isoforms of which have been clearly linked genetically to AD, but the mechanism by which these isoforms either promote or suppress AD is not known. Because LRP has so many different ligands that could be causing many of the adverse effects seen in AD, these investigators propose to undertake careful biophysical experiments to understand ligand binding and ligand competition for LRP. The aims of the proposed research are: (1) Express and characterize soluble fragments of the LRP extracellular subdomains. LRP has three repeated subdomains, each of which resembles the LDL receptor extracellular domain. These investigators will express each of these as well as smaller fragments of each in P. pastoris yeast. (2) Determine which LRP ligands compete for overlapping binding sites by ligand blotting. (3) Determine the smallest region of the LRP extracellular domain that bind to thrombin-PNlapoE, and PNII. (4) Characterize the kinetics of ligand binding using BIAcore. In particular, we will probe the role of hepara sulfate proteoglycans in the reaction. (5) Determine the structures of minimal fragments of LRP ligands bound to minimal fragments of the LRP extracellular domain.